As regards the present invention, low-altitude flight is taken to mean flight along a flight trajectory (at low altitude) that allows an aircraft to follow as closely as possible the terrain being over-flown, in particular to avoid being detected. Such a low-altitude flight trajectory is therefore situated at a predetermined height above the terrain, for example 500 feet (around 150 meters).
By reason of this proximity to the ground, any lateral or downward vertical swerve (beyond a certain safety margin) of the aircraft, with respect to the flight trajectory to be followed, as the aircraft is guided along said flight trajectory, presents a high risk of collision with the terrain being over-flown (directly with the ground or with a construction or an element situated on said ground). Of course, the existence of such a risk is not acceptable.